1. Field of the Invention
The present invention relates to packet switching communication and ATM switching communication, and particularly to a routing control system.
2. Description of the Related Art
In connection-oriented communication as represented by ATM (Asynchronous Transfer Mode), one connection is established in one manner at the time of setting up a call and no change is allowed during a call. The application program communicates to the base (communication partner) using this ATM connection. Here, as one means of altering a route in response to congestive state in the network, one routing control method has been proposed by which a plurality of connections from source to destination are set up independently and the connections employed are altered for every information unit (message). The selection of connections at this time is executed only at the transmission node which is the information source. Devices such as terminals, information transfer servers, and routers that become information sources and transmit information are here-inbelow referred to as "transmission terminals."
In a case in which a transmission terminal transmits an information group made up of a plurality of information units from source to destination by a plurality of routes using a plurality of connections, one connection is used for each information unit transmitted. The plurality of connections that are set up for transmitting from source to destination by a plurality of routes are called the same connection group.
At this time, the ID of the VC (virtual channel) (hereinbelow referred to as "VCI"), or the ID of the VP (virtual path) (hereinbelow referred to as "VPI"), which are the identifiers of each connection, is required at each link (segment) between connection nodes.
FIG. 1 shows a routing table for a routing system of the prior art. In the routing table shown in FIG. 1, the input-side VCI are mapped to the output-side VCI. In other words, this table is a correspondence table such that VCI or VPI which are the ID of input packets (hereinbelow referred to simply as "input-side VCI"), are rewritten as the VCI or VPI which are the ID of output packets (hereinbelow referred to simply as "output-side VCI"). This means that, for example, a packet for which input side VCI=100 is rewritten as output side VCI=200 and outputted from the switch. In FIG. 1, one input-side VCI is mapped to one output-side VCI.
The first problem of the above-described prior art is the occurrence of a reduction in network throughput and communication quality degradation including delays and cell loss.
The cause of this problem is that, in general, when a network is very large, transmission nodes cannot accurately detect congestive states in the network, due to propagation delay and other factors, so that dynamic selection of optimum routes for good routing efficiency cannot be expected.
A second problem of the prior art is that the VCI and VPI required at each link (segment) between connection nodes are consumed in large volumes due to the plurality of connections used.
The reason for this is that only a limited number of these VCI and VPI are prepared, and, due to the concern that VCI and VPI will be exhausted because of the plurality of VCI and VPI consumed when using a plurality of connections, VCI and VPI must be conserved to ensure effective use of the network.